IBM AIX Continuous Availability Features - IBM Redbooks

when combined with hot spare disk and hot swap disks, allows for maintenance to take place
without requiring any planned down time.
However, although LVM mirroring does increase storage availability, it is not intended to be a
substitute for system backup. Additional detailed information about LVM mirroring is available
in the mirrorvg man page and in AIX 5L Version 5.3 System Management Concepts:
Operating System and Devices Management, SC23-5204.
Hot spare disks in a volume group
Beginning with AIX V5.1, the ability to designate hot spare disks for an LVM mirrored volume
group was added. LVM hot spare allows automatic migration of partitions from a failing disk to
another free disk previously assigned as a hot spare. The hot spare disk feature is an
operating system equivalent to that of a hot spare disk when using a RAID storage solution
that most storage administrators are already familiar. Hot spare disk concepts and policies
are described in AIX 5L Version 5.3 System Management Concepts: Operating System and
Devices Management, SC23-5204.
The chvg feature for sync
There is a feature in LVM to set the synchronization characteristics for the volume group
specified by the VolumeGroup parameter that either permits (y) the automatic
synchronization of stale partitions or prohibits (n) the automatic synchronization of stale
partitions. This flag has no meaning for non-mirrored logical volumes.
Automatic synchronization is a recovery mechanism that will only be attempted after the LVM
device driver logs LVM_SA_STALEPP in the errpt. A partition that becomes stale through any
other path (for example, mklvcopy) will not be automatically resynced. This is always used in
conjunction with the hot spare disk in a volume group feature.
To change the volume group characteristics, you can use the smitty chvg SMIT fastpath, or
you can use the following commands (these are examples):
/usr/sbin/chvg -s'y' fransvg
/usr/sbin/chvg -h hotsparepolicy -s syncpolicy volumegroup
Advanced RAID support
Most common storage subsystems today are RAID arrays defined into multiple logical units
(LUNs) that ultimately represent a disk definition to AIX. When additional space is required,
you can choose to expand the size of a current LUN, as opposed to adding an additional
LUN. This ultimately results in changing the size of a previously-defined disk.
In order to use this space, the disk must grow in size by dynamically adding additional
physical partitions (PP). AIX V5.2 introduced support of dynamic volume expansion by
updating the chvg command to include a new -g flag. More detailed information about this
topic is available in the man page for chvg and in AIX 5L Differences Guide Version 5.2
Edition, SG24-5765.
Portability of volume groups
One useful attribute of LVM is a user’s ability to take a disk or sets of disks that make up a
volume group to another AIX system and introduce the information created on the first
machine onto the second machine. This ability is provided through the Volume Group
Descriptor Area (VGDA) and the logical volume control block (LVCB).
The design of LVM also allows for accidental duplication of volume group and logical volume
names. If the volume group or logical volume names being imported already exist on the new
machine, then LVM will generate a distinct volume group or logical volume name.
Chapter 2. AIX continuous availability features 43